The whole point is to not bankrupt yourself. Is there some lost DPS potential there? Yes, but we're talking about 40 average potency on DA/Souleater versus Delirium Combos. Only having Dark Dance and Dark Mind to worry about cool down wise is easily subsidized in the grand scheme. Dark Passengers blind is useless on most bosses, and you have to decide if you want to use C&S to gain MP or lose MP and deal damage.

Syphon Strike refunds half a Dark Arts, same with C&S, and for slow hitting bosses, like Floor 1, the damage on tank is really low I typically drop Grit and Blood Weapon to get back to 100%.